(CG 2/21). That it belongs to God alone to create (Book 2: God The Origin of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

As creation is the work of God alone, so whatever beings are producible only by creation must be immediately produced by Him. Such are all spirits, the existence of which for the present let us suppose, and likewise all bodily matter. These several existences are immediate effects of creative power. Now power is not determined and limited to one effect, when it is productive of several effects immediately, and that not out of any pre-existent material. I say 'immediately,' because if the production were through intermediate agents, the diversity of effects might be ascribed to those intermediate causes. I say again 'not out of any pre-existent material,' because the same agent by the same action causes different effects according to the difference of material. God's power then is not determined and limited to one effect.

2. Every perfect active power is co-extensive with and covers all cases of its own proper effect: thus perfect building power would extend to everything that could be called a house. But the divine power is of itself the cause of being, and being is its proper effect. Therefore that power extends to all things that are not inconsistent with the idea of being: for if the divine power were available only for one particular effect, it would not be the ordinary cause of being, as such, but cause of 'this being.' Now what is inconsistent with the idea of 'being' is the opposite of 'being,' which is 'not-being.' God then can do all things that do not include in themselves the element of not-being, that is to say, that do not involve a contradiction.

3. Every agent acts inasmuch as it is in actuality. According then to the mode of actuality of each agent in the mode of its active power. Now God is perfect actuality, having in Himself the perfections of all beings (B. I, Chap. XXVIII): therefore His active power extends to all things that are not inconsistent with actual being.

5. There are three ways in which an effect may not be in the power of an agent. In one way, because it has no affinity or likeness to the agent, for every agent acts to the production of its own likeness somehow: hence man cannot be the parent of brute or plant, though he can be parent of man, who is more than they. In another way, on account of the excellence of the effect, transcending the compass of the active power: thus the active power of matter cannot produce spirit. In a third way, on account of the material being determined to some effect, and the agent having no power over it: thus a carpenter cannot make a saw, because his art gives him no power over iron. But in none of these ways can an effect be withdrawn from the divine power: not for the unlikeness of the effect, since every being, in so much as it has being, is like God (Chap. XV): nor again for the excellence of the effect, since God is above all in goodness and perfection (B. I, Chapp. XXVIII, XLI): nor lastly for the defect of the material, since God in His action needs no material (Chap. XVI).

This also is taught by divine Scripture as a tenet of faith. I am God Almighty, walk before me and be perfect (Gen. xvii, 1): I know that you can do all things (Job xlii, 2): No word shall be impossible with God (Luke i, 37).

Hereby is excluded the error of sundry philosophers, who have laid it down that God can do nothing except according to the course of nature. On such it is said: As though the Almighty had no power, they reckoned of him (Job xxii, 17).